30 GENERAL HISTORY OP 



in it, becomes frozen, and is placed under a microscope, 

 in a cold situation. Dr. Ehrenberg states that if the ice be 

 clear, each animalcule or group will evidently be sur- 

 rounded by an exceedingly small portion of water, which 

 that naturalist supposes to be occasioned by the superior 

 temperature or animal heat of the creatures preventing 

 congelation ; and he is of opinion^ that in all cases where 

 this portion of the water freezes, the animalcule neces- 

 sarily dies. 



If the water containing polygastric Infusoria be gra- 

 dually raised to a temperature of even 125^^ of Fah. these 

 creatures w^ill live ; and Dr. E. observes, that some of the 

 Chlamidomonas pulvisculus existed, on one occasion, in 

 water at 200° of Fah. If the increase of temperature be 

 sudden, the animalcules die at 140°, notwithstanding it 

 be kept up for only half a minute. 



Section VII. — Effects of Air, Chemical Mixtures, and 

 Poisons y on Infusoria > 



That animalcules, like every other part of the animal 

 creation, continually require fresh supplies of atmospheric 

 air for their support, may be deduced from a variety 

 of experiments. If a thin pellicle of oil be spread 

 over the surface of the water in which they are retained, 

 they very soon die from exhaustion ; and indeed, it must 

 have often happened to those who are in the habit of 

 collecting Infusoria, that when the cork has been left, by 

 accident, too long in a phial full of water, they have ex- 

 perienced this mishap. This is especially the case with 



